/Engine/Source/Runtime/Engine/Public/Elements/SMInstance/SMInstanceElementId.h
This may be called with INDEX_NONE as the PreviousInstanceIndex value if the element had previously been unmapped, but was mapped again via serialization (eg, via an undo/redo).
typedef TMulticastDelegate_ThreeParams< void, const [FSMInstanceElementId](API\Runtime\Engine\Elements\SMInstance\FSMInstanceElementId) &, int32, int32 > FOnInstanceRemapped